vp8: Replace x*155/100 by x*101581>>16.

Idea stolen from webp (by Pascal Massimino) - because it's Cool.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavcodec/vp8.c

@@ -249,12 +249,13 @@ static void get_quants(VP8Context *s)
         } else
             base_qi = yac_qi;
 
-        s->qmat[i].luma_qmul[0]    =       vp8_dc_qlookup[av_clip_uintp2(base_qi + ydc_delta , 7)];
-        s->qmat[i].luma_qmul[1]    =       vp8_ac_qlookup[av_clip_uintp2(base_qi             , 7)];
-        s->qmat[i].luma_dc_qmul[0] =   2 * vp8_dc_qlookup[av_clip_uintp2(base_qi + y2dc_delta, 7)];
-        s->qmat[i].luma_dc_qmul[1] = 155 * vp8_ac_qlookup[av_clip_uintp2(base_qi + y2ac_delta, 7)] / 100;
-        s->qmat[i].chroma_qmul[0]  =       vp8_dc_qlookup[av_clip_uintp2(base_qi + uvdc_delta, 7)];
-        s->qmat[i].chroma_qmul[1]  =       vp8_ac_qlookup[av_clip_uintp2(base_qi + uvac_delta, 7)];
+        s->qmat[i].luma_qmul[0]    =           vp8_dc_qlookup[av_clip_uintp2(base_qi + ydc_delta , 7)];
+        s->qmat[i].luma_qmul[1]    =           vp8_ac_qlookup[av_clip_uintp2(base_qi             , 7)];
+        s->qmat[i].luma_dc_qmul[0] =       2 * vp8_dc_qlookup[av_clip_uintp2(base_qi + y2dc_delta, 7)];
+        /* 101581>>16 is equivalent to 155/100 */
+        s->qmat[i].luma_dc_qmul[1] = (101581 * vp8_ac_qlookup[av_clip_uintp2(base_qi + y2ac_delta, 7)]) >> 16;
+        s->qmat[i].chroma_qmul[0]  =           vp8_dc_qlookup[av_clip_uintp2(base_qi + uvdc_delta, 7)];
+        s->qmat[i].chroma_qmul[1]  =           vp8_ac_qlookup[av_clip_uintp2(base_qi + uvac_delta, 7)];
 
         s->qmat[i].luma_dc_qmul[1] = FFMAX(s->qmat[i].luma_dc_qmul[1], 8);
         s->qmat[i].chroma_qmul[0]  = FFMIN(s->qmat[i].chroma_qmul[0], 132);